Wafer inspection systems help a semiconductor manufacturer increase and maintain integrated circuit (IC) chip yields by detecting defects that occur during the manufacturing process. One purpose of inspection systems is to monitor whether a manufacturing process meets specifications. The inspection system indicates the problem and/or the source of the problem if the manufacturing process is outside the scope of established norms, which the semiconductor manufacturer can then address.
Evolution of the semiconductor manufacturing industry is placing ever greater demands on yield management and, in particular, on metrology and inspection systems. Critical dimensions are shrinking while wafer size is increasing. Economics is driving the industry to decrease the time for achieving high-yield, high-value production. Thus, minimizing the total time from detecting a yield problem to fixing it determines the return-on-investment for the semiconductor manufacturer.
A normalized cross-correlation (NCC) between the optics patch containing the pattern of interest (POI) and a template POI image that is randomly picked from one sample image can be used for POI image registration. Every POI image is aligned with the same template. If the randomly chosen template is a robust representation for this POI image population, this method may be valid for POI registration.
However, NCC die-to-die inspection does not consider the effects of POI vicinity design patterns. This is because, when comparing POI images from two adjacent dies, the common noise caused by the same vicinity cancels out. This may not be true for intra-die inspection where POI could occur anywhere within a die and could have different vicinity patterns. In that case, the POI images could be contaminated by the different vicinity design patterns. Thus, it may be important to analyze and reduce the noise induced by vicinity design patterns.
It can be difficult to tell whether the NCC method for POI images registration is adequate because the template is chosen randomly. If the template POI image has noise or defects, then aligning other POI images with it could cause misalignment errors.
For die-to-die, reference image and test image from adjacent dies are assumed to be aligned. If there is offset for the POI, the offset is the same for the two. Thus, the offset will not hurt the difference image. However, for intra-die, each POI has a different location and surrounding, which need to be verified as aligned. Otherwise, comparison is difficult or even impossible.
If the POI is too small or has insufficient geometry, it may not be a good registration target. The NCC method may fail for high demanding intra-die comparison tasks.
POI vicinity induced noise is canceled out in die-to-die inspection since both instances have the same vicinity of patterns. However, this is not true for intra-die inspection because vicinity pattern differences are an additional noise source for it.
Therefore, improved defect review techniques and, more particularly, improved intra-die inspection techniques are needed.